package org.hcf.utils.randomGuid;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

/**
 * 利用当前时间、随机数及IP地址生成一个全球唯一号
 * @author hcf
 * @email hcf0108@163.com
 * @create 2019-02-28 下午 3:19
 **/
public class RandomGuid {
    public static final String GUID_BLANK = "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF";
    public static final int GUID_LEN = GUID_BLANK.length();
    public String valueBeforeMD5 = "";
    public String valueAfterMD5 = "";
    private static Random myRand;
    private static SecureRandom mySecureRand;

    private static String s_id;

    static {
        mySecureRand = new SecureRandom();
        long secureInitializer = mySecureRand.nextLong();
        myRand = new Random(secureInitializer);
        try {
            s_id = InetAddress.getLocalHost().toString();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
    }

    /**
     * Default constructor.  With no specification of security option,
     * this constructor defaults to lower security, high performance.
     */
    public RandomGuid() {
        getRandomGUID(false);
    }

    /**
     * Constructor with security option.  Setting secure true
     * enables each random number generated to be cryptographically
     * strong.  Secure false defaults to the standard Random function seeded
     * with a single cryptographically strong random number.
     */
    public RandomGuid(boolean secure) {
        getRandomGUID(secure);
    }

    /**
     * Method to generate the random GUID
     * @param secure
     */
    private void getRandomGUID(boolean secure) {
        MessageDigest md5 = null;
        StringBuffer sbValueBeforeMD5 = new StringBuffer();

        try {
            md5 = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }

        try {
            long time = System.currentTimeMillis();
            long rand = 0;

            if (secure) {
                rand = mySecureRand.nextLong();
            } else {
                rand = myRand.nextLong();
            }

            // This StringBuffer can be a long as you need; the MD5
            // hash will always return 128 bits.  You can change
            // the seed to include anything you want here.
            // You could even stream a file through the MD5 making
            // the odds of guessing it at least as great as that
            // of guessing the contents of the file!
            sbValueBeforeMD5.append(s_id);
            sbValueBeforeMD5.append(":");
            sbValueBeforeMD5.append(Long.toString(time));
            sbValueBeforeMD5.append(":");
            sbValueBeforeMD5.append(Long.toString(rand));

            valueBeforeMD5 = sbValueBeforeMD5.toString();
            md5.update(valueBeforeMD5.getBytes());

            byte[] array = md5.digest();
            StringBuffer sb = new StringBuffer();
            for (int j = 0; j < array.length; ++j) {
                int b = array[j] & 0xFF;
                if (b < 0x10) sb.append('0');
                sb.append(Integer.toHexString(b));
            }

            valueAfterMD5 = sb.toString();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }


    /**
     * Convert to the standard format for GUID
     * (Useful for SQL Server UniqueIdentifiers, etc.)
     * Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6q
     */
    public String toString() {
        String raw = valueAfterMD5.toUpperCase();
        StringBuffer sb = new StringBuffer();
        sb.append(raw.substring(0, 8));
        // sb.append("-");
        sb.append(raw.substring(8, 12));
        // sb.append("-");
        sb.append(raw.substring(12, 16));
        // sb.append("-");
        sb.append(raw.substring(16, 20));
        // sb.append("-");
        sb.append(raw.substring(20));

        return sb.toString();
    }

    /**
     * Demonstraton and self test of class
     */
//    public static void main(String args[]) throws Exception {
//        System.out.println("Please enter 'return' for get a unid, 'q' to quit.");
//        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
//        String input = "";
//        do{
//            input = br.readLine();
//            if(!input.equalsIgnoreCase("q")){
//                RandomGuid myGUID = new RandomGuid();
//                System.out.println(myGUID.toString());
//            }
//        }while(!input.equalsIgnoreCase("q"));
//    }
}
